This invention relates generally to methods and apparatus for interactive defining regions of interest for creating computed tomographic (CT) images, magnetic resonance (MR) images, and x-ray (XR) images, and more particularly to methods and apparatus for defining such regions around tortuous structures.
In at least some computed tomography (CT) imaging system configurations, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the xe2x80x9cimaging planexe2x80x9d. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal spot. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator adjacent the collimator, and photodetectors adjacent the scintillator.
CT, MR and XR routinely produce 3D data sets. Analyzing tortuous structures, such as airways, vessels, ducts or nerves is one of the major applications of these devices. Known methods and apparatus for accomplishing such analysis use multiple oblique slices to analyze local segments of these structures. The multiple oblique slice views provide clear, undistorted pictures of short sections of tortuous structures, but rarely encompass their full length.
Curved reformation images also provide synthetic views of tortuous structures, and advantageously capture the whole length of these objects. Thus, curved reformation images are well suited to analysis of such structures. True 3D length measurements along an axis of a tortuous structure can be obtained from these views, and measurements from these views are sufficiently close to the real anatomy in many cases. However, those synthetic views are limited to a single voxel depth and therefore contain less information about the anatomy than a full 3D view.
In one known technique, curved reformation images are generated by sampling values along a curve at equidistant points to generate lines, and then translating the curve using a sampling vector to generate the next image line (i.e., along any 2D orientation). By representing the points in a polar coordinate system, with all of the points in the upper two quadrants of the coordinate system, a cubic spline algorithm is applied to a redefined set of points, thereby generating a series of functions that best approximates a desired curve. A conversion is then done to generate screen coordinates for selecting pixel values to display. Also, additional curves equidistant from an original curve are generated to produce additional views of the scanned structure. The calculation of these additional curves also uses a polar coordinate representation of cubic spline coefficients for the initial curve. These coefficients are used to determine intermediate data points at which a uniform length perpendicular is constructed. New data points equidistant from the initial curve are calculated by traversing each perpendicular a desired length.
Such known techniques and systems do not provide for user-friendly interactive creation of regions of interest well-suited to the display of tortuous structures. For example, in some known implementations, a curve is translated interactively but artifacts are created in the case of tortuous structures because the sampling curve may be outside of the object. These artifacts look like pseudo-stenoses.
To display some features, for example, bifurcations, local stenoses, and calcifications, one must manually redefine a sampling vector. This process is time consuming. Also, it is difficult to adjust the display to depict selected features. Also, the display assumes that the target features are known when the sampling vector is selected. Therefore, this known method is not practical for medical review because the possible lesions are not known ahead of time.
In one aspect, a method for interactively creating a region of interest of a reconstructed image is provided. The method includes defining a thickness value, defining a polygon, and defining a 3D projection geometry. The method also includes defining a vector perpendicular to a line of sight which is defined by the 3D projection geometry, swiping the vector along the polygon to create a surface of interest, and displaying three dimensionally a plurality of points wherein a distance from the points to the created surface along the line of sight is approximately the defined thickness value or less.
In another aspect, a method for interactively creating a region of interest of a reconstructed image is provided. The method includes defining a thickness value, defining a polygon, and defining a 3D projection geometry. The method also includes defining a vector perpendicular to a line of sight which is defined by the 3D projection geometry, swiping the vector along the polygon to define a surface, and swiping the surface along the line of sight to create a volume of interest. The method also includes intersecting the volume of interest with a three dimension data set, and three dimensionally displaying the intersection.
In a further aspect, a scanning system is provided. The scanning system includes a radiation source, a radiation detector positioned to receive radiation emitted from the source, and a processor operationally coupled to the detector. The processor is configured to receive a thickness value, define a polygon, and receive a 3D projection geometry definition. The processor is further configured to define a vector perpendicular to a line of sight which is defined by the 3D projection geometry, swipe the vector along the polygon to create a surface of interest, and display three dimensionally a plurality of points wherein a distance from the points to the created surface along the line of sight is approximately the defined thickness value or less.
In still a further aspect, a scanning system includes a radiation source, a radiation detector positioned to receive radiation emitted from the source, and a processor operationally coupled to the detector, wherein the processor is configured to receive a thickness value, and define a polygon. The processor is also configured to define a 3D projection geometry, define a vector perpendicular to a line of sight which is defined by the 3D projection geometry, and swipe the vector along the polygon to define a surface. The processor is also configured to swipe the surface along the line of sight to create a volume of interest, intersect the volume of interest with a three dimension data set, and display three dimensionally the intersection.